This invention relates to a push button switch which is put into an ON state (or an OFF state) when an operating portion is pushed and then put into an OFF state (or an ON state) when the operating portion is pushed again.
A conventional push button switch of the type described is illustrated in FIGS. 1 and 2. A push button 1 is mounted on a housing 3 to be movable along an axial direction. The push button 1 is urged by a first spring 4 in an upward direction in FIGS. 1 and 2. The push button 1 has a guide chamber 5 which is formed at a position offset from a center axis of the push button 1. A movable contact 2 is mounted on a sleeve 6 which is movably inserted into the guide chamber 5. A second spring 7 is for urging the movable contact 2 towards a fixed contact 8 (in a downward direction in the figures).
The second spring 7 is substantially fully relaxed when the push button 1 is not pushed down, namely, in an OFF state. In this condition, an urging force for urging the movable contact 2 towards the fixed contact 8 is substantially equal to zero. The movable contact 2 is surrounded by a cylindrical rubber contact 9. The rubber contact 9 is for isolating the movable contact 2 from the fixed contact 8 when the urging force of the second spring 7 is equal to zero. The push button 1 is further provided with a heart cam (not shown). The housing 3 is provided with a pin 10 travelling along an outer periphery of the heart cam.
The heart cam comprises a cam plate having a recess formed on the upper side thereof. When the push button 1 is pushed down, the pin 10 is relatively upwardly moved along the outer periphery of the heart cam to be engaged with the recess of the heart cam. Thus, the push button 1 is held in a depressed position at a predetermined distance. When the push button 1 is pushed again, the pin 10 is released from engagement with the recess of the heart cam to thereby bring the push butt, on 1 into a free state.
In the push button switch of the above-mentioned structure, when the push button 1 is pushed in an OFF state, the first and the second springs 4 and 7 are compressed. The sleeve is moving downwardly by the urging force of the second spring 7. In this event, the rubber contact 9 is deformed to allow the movable contact 2 to be brought into contact with the fixed contact 8. On the other hand, the pin 10 is engaged with the recess of the heart cam to hold the push button 1 in the depressed position. Thus, the contacts are held in an ON state.
When the push button 1 is pushed again, the pin 10 is released from engagement with the recess of the heart cam after the first and the second springs 4 and 7 are slightly deformed. Subjected to the elastic restoring force of the first and the second springs 4 and 7, the push button 1 is moved upwardly. As a result, the second spring 7 is substantially fully relaxed and therefore loses the urging force for urging the movable contact 2 downwards. The movable contact 2 is moved away from the fixed contact 8 by the elastic restoring force of the rubber contact 9. Thus, the contacts are put into an OFF state.
In the above-mentioned push button switch, the push button 1 is pushed down to compress the second spring 7. The second spring 7 exerts the urging force to bring the movable contact 2 into contact with the fixed contact 8. In order to put the switch into an ON state, an operator must push down the push button 1 with a pressing force sufficient to compress the first and the second springs 4 and 7. Thus, the pressing force required to the operator inevitably becomes large.